Radio receivers accept and process radio frequency (RF) transmitted energy signals to yield, generally, audible or visual information. Typically, the originally received RF signal will be converted to an intermediate frequency (IF) signal prior to reducing the desired signal information yet further to audio levels. Various signal processing functions may occur at the IF level, including signal attenuation as may be necessary to prevent the signal from exceeding a threshold level. Additionally, attenuation may be performed on a received signal to cancel a number of distortion products gained during transmission.
FIG. 1 illustrates a constant impedance attenuator circuit (100) according to the prior art. Traditional constant impedance attenuator circuits are usually based on a classic PI or T circuit. The PI circuit illustrated in FIG. 1 may be selected as it can have better high frequency, wide bandwidth behavior when compared to a T circuit. As shown in FIG. 1, a constant impedance attenuator (100) may include a signal input (110) and a signal output (120). Additionally, a series resistive element (130) and a pair of shunt resistive elements (140, 150) may be coupled to the circuit as illustrated in FIG. 1. For an attenuator with equal input and output impedances, the shunt elements (140, 150) have equal values. The absolute impedance values and the ratio of the shunt and series values determine the impedance and the attenuation value imposed onto received RF signals.
While the constant impedance fixed attenuator circuit (100) illustrated in FIG. 1 is effective for input signals having a constant level, this is often not the case with a received signal. Rather, received signals and their uses often require variable attenuation levels and tight tilt specifications.